Actin and myosin based motile systems are involved in a wide range of cellular motile functions including organelle transport, ameboid motion and cell division. Many types of myosin have been discovered all of which share a common enzymatic motor domain with actin binding and ATP hydrolytic activity. However, the neck regions differ in length and their ability to bind light chains. This proposal is concerned with a recently discovered myosin, Myosin V (M5). M5 has an elongated neck region with the potential to bind six light chains. It has been proposed that the neck acts as a rigid level arm that produces movement and force that produces movement and force by amplifying small movements in the motor domain. In this proposal the level arm hypothesis will be tested by testing mutant M5 molecules with varying neck lengths. In mice and humans, several mutations that affect neural function and pigment deposition have been identified. These mutations suggest a role for M5 in organelle transport. Organelle motors are typically processive. In this proposal it will be determined if a single M5 molecule is processive by studying its ability to take multiple steps on an actin track per diffusional encounter.